The present invention relates to a Kohler illuminating device for microscopes in which an end surface of a light-guide serves as a uniform, increased-area source of secondary light.
Microscope illuminating systems which use light guides have been known for a long time. The advantage of such illuminating systems resides, on the one hand, in their ease of handling and, on the other hand, in the thermal decoupling of the source of light, which is separated in space from the instrument and flexibly connected to it. Few fiber-optical microscope illuminating systems are, however, constructed in accordance with the Kohler principle which constitutes a basic prerequisite for microscopic work of high quality.
From West German published patent application No. OS 27 36 319 (Frosch et al.) of Feb. 22, 1979, a fiber-optical Kohler illuminating device for microscopes is known in which fiber optics is used to make the luminous density uniform in the object plane. For this purpose, radially displaceable diaphragms or diaphragms with radially extending absorption are arranged on the lamp side in front of the light guide in a plane conjugated to the object plane. This diaphragm arrangement is very sensitive to adjustment and this has a negative effect on the cost of manufacture and the reliability of the illuminating device. No special measures have been taken to make the luminous density in the aperture planes uniform and no information is given as to the three-dimensional structural development of the system.
In West German published patent application No. OS 27 20 650 (Bufe et al.) of Dec. 1, 1979, another illuminating device based on the Kohler principle is described. The distances between light, lamp collector and light-guide entrance surface are selected in such a manner that the distribution of the luminous density in the pupils of the illuminating beam takes place. The light-guide end surface is followed by the known Kohler optical system with collector, illuminating-field diaphragm and aperture diaphragm, which is arranged as customary in the rear focal plane of the following condenser.
Now, as a rule transmitted-light microscopes are constructed in the manner that the luminous-field diaphragm is located in the base of the stand on which the lamp housing is attached, while the aperture diaphragm is located directly in the rear focal plane of the condenser, which is arranged below the microscope stage. In the case of incident-light microscopes the illuminating device, on the other hand, is placed on the tube carrier of the microscope arm and an intermediate focusing of the source of light is effected, in the plane of which the aperture diaphragm is arranged in front of the illuminating-field diaphragm in the path of the light, since the rear focal plane of the objective which serves as condenser is generally not accessible. Incident-light illuminating devices are therefore relatively long and require support by the microscope if stability is important. Therefore, up to now different optical systems have been used for incident-light and transmitted-light illuminations, only individual components of which, such as for instance the lamp housing, are compatible with each other.